Treatment of casein fibers



UNITED STATES iieierete TREATMENT OF CASEIN FIBERS Theodoor Koch,Odsterbeek,

and Henricus Anthonius van der Kroon, Arnhem, Netherlands, assignors toAmerican Enka Corporation, Enka, N. 0., a firm No Drawing. ApplicationApril 22, 1938, Serial No. 203,700. In Germany May 11, 1937 7 Claims.

to reduce their swelling property by treatment with aldehydes or withsubstances which give rise to aldehydes for example with formaldehyde orhexamethylenetetramine.

We have previously proposed to improve casein threads hardened asdescribed above by neutralising any carboxyl groups remaining in themolecule by treatment for example with alkaline earths. In this way aproduct is obtained which possesses resistance to boiling water andwhich may thus be dyed in a hot neutral dye bath.

When, however, such casein fibers either alone or mixed with wool are tobe treated in an acid medium or even in a dye bath containing chromicacid, the casein fibers are attacked and the material becomes slimyduring the dyeing process and shrinks and sticks together during thesubsequent drying operation.

We have now found that casein fibers may be rendered resistant even tohot acid dye baths by subjecting the fibers to treatment with nitrousacid in addition to treating them with aldehydes such as formaldehyde.

The present invention accordingly comprises a process for renderingcasein fibers resistant to shrinkage or sticking in hot acid dye bathswhich consists in subjecting the fibers which have not previously beenneutralised with alkaline reagents to treatment with nitrous acid andwith an aldehyde or a substance giving rise to an aldehyde.

The treatment with nitrous acid may be varied in degree so that varyingdegrees of resistance to hot acid baths may be secured.

The source of nitrous acid may conveniently consist of an alkalinenitrite such as sodium nitrite and an acid, for example, glacial aceticacid. Alternatively the nitrous acid may be formed in situ by thereaction of acid groups in the casein with the added alkaline nitrite,e. g., sodium nitrite.

After the hardening treatment, any free carboxyl groups remaining in thecasein molecule may if desired be neutralised as previously proposed.

It is desirable that the treatment of the fibers with nitrous acidshould not be carried to excess since yellowing of the fiber thenoccurs. Any such yellowing produced may however be removed, by treatmentof the fibers with a reducing bleaching agent such, for example, assodium hyposulphite (Na2S2O4).

The nitrite treatment may conveniently be carried out by subjecting thecasein fibers to a mixture of a solution of alkaline nitrite and aneutral dehydrating salt such as sodium sulphate or magnesium sulphate.

After treatment of the fibers with an aldehyde and with nitrous acidthey may subsequently be treated with a softening agent such asglycerol,

sulphonated oils, sulphonated fatty alcohols or other substancesnormally employed for that purpose.

Following is a description by way of example of several methods ofcarrying the invention into efiect.

Example I Casein fibers produced from. an alkaline casein solution inknown manner by means of an acid precipitating bath are thoroughlyhardened with a 10% solution of formaldehyde. After washing and dryingthe fibers are treated at room temperature for two hours with a solutioncontain- Y ing 8 grins. of sodium nitrite and. 11 grms. of glacialacetic acid per 100 grins. of dried fiber. The fibers are then wellwashed and dried.

If fibrous material thus treated is dyed for an hour at C. in a dye bathcontaining 4% of sulphuric acid with a bath ratio of 1 to 40 calculatedon the weight of the fibrous'material,

practically no shrinkage or sticking together of the fibers occurs. Inthe absence of treatment with nitrous acid and under similar conditionsof dyeing, a tender, brittle product which is stuck together isobtained.

Example II Casein threads spun from a casein solution in the knownmanner are treated under tension with a solution. containing 3% ofnitrous acid and 8% of sodium sulphate. The excess of nitrous acid isremoved by washing with water and the threads are then hardened withformaldehyde in the usual manner.

Example III Search am solutions and the like.

Finally it is well washed and dressed with a 0.2% solution ofBrillantavirol.

The casein fibers treated as described above possess good resistance tohot acid wool-dyeing baths which may contain sulphuric acid but they areinferior to ordinary wool when they are subjected to an after-treatmentand washing with weakly alkaline agents such as sodium carbonate Undersuch treatment the casein fibers exhibit excessive swelling andslipperiness.

It has now further been found that in addition to producing a goodresistance to hot acid wooldyeing baths the above-mentioned swelling andslipperiness when employing alkaline aftertreatment baths such as sodiumcarbonate may be avoided by applying to the casein fibers solublenitrites without employing a special addition of acid. In such a case itwould appear that the acid properties of the casein are just sufficientto liberate gently and gradually the necessary quantity of nitrous acidfrom the nitrites and to cause it to act on the fibers in thecharacteristic man-- ner above described. This gentle and slow actionappears to be of great importance in determining the behaviour of thetreated casein fibers to alkaline washing baths, for example, solutionsof sodium carbonate. It has been found that whereas casein stillcontaining acid groups is capable of reacting with alkaline nitrites togive the advantageous results above referred to, casein neutralisedbeforehand with alkaline agents, such as alkaline earths, e. g., calciumhydroxide solution, is not capable of so acting.

When the nitrite treatment is to be applied to highly swollen caseinthreads it is advantageous to add to the nitrite bath considerablequantities of dehydrating neutral salts such as sodium sulphate,magnesium sulphate and the like.

Example IV Casein fibers spun in a manner known per se in an acid'bathand pro-hardened with formaldehyde and dried are introduced into anaftertreatment bath containing 7% of sodium nitrite and if desired 10%of sodium sulphate and are treated therein at room temperature for twohours at a bath ratio of 1 to 30. The material is then thoroughlyhydro-extracted, washed and dried.

The nitrite solution may also be allowed to act on the casein fiberbefore the first drying and in such a case the formaldehyde treatmentmay be carried out before or after the nitrite treatment.

Having now set forth the invention as required by the patent statutes,what is claimed is:

1. In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoagulated in an acid precipitating bath, the step which comprisessubjecting the fibers to treatment with nitrous acid.

2. In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoagulated in an acid precipitating bath, the steps which comprisehardening the fibers with an aldehyde solution and then subjecting thesame to treatment with nitrous acid.

3. In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoagulated in an acid precipitating bath, the steps which comprisesubjecting the fibers to treatment with a solution of nitrous acid andsodium sulphate, washing the fibers to remove the excess nitrous acidand thereafter hardening the same with formaldehyde.

' 4; In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoagulated in an acid precipitating bath, the steps which comprisehardening the fibers with a solution of formaldehyde, Washing and dryingthe fibers, preparing a solution of sodium nitrite and acetic acid andtreating the fibers with the same, and again washing and drying thefibers.

5. In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoagulated in an acid precipitating bath, the step which comprisessubjecting the fibers to treatment with nitrous acid by preparing asolution of an alkaline nitrite and impregnating the fibers therewith,and effecting liberation of nitrous acid by reacting said nitrite withthe acid groups in the fibers.

6. In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoa ulated in an acid precipitating bath, the steps which comprisehardening the fibers with a formaldehyde solution and drying the same,treating the fibers in a bath containing sodium nitriteand a neutraldehydrating salt and again washing and drying the same.

'7. In a process for rendering casein fibers resistant to shrinkage andsticking in hot acid dye baths wherein the fibers have been initiallycoagulated in an acid precipitating bath, the steps which comprisehardening the fibers with a solution of formaldehyde, washing and dryingthe same, treating the fibers with a solution of sodium nitrite andacetic acid, bleaching the thus treated fibers with a weak solution ofsodium hyposulphite and finally neutralizing the residual carboxylgroups in the fibers with a saturated solution of lime, washing anddressing the same with a softening agent.

THEODOOR KOCH. HENRICUS ANTHONIUS VAN DER KROON.

